It is proposed to examine the net ion movements induced in Halobacterium halobium envelope membrane vesicles on illumination in the presence and absence of amino acids. An attempt will be made to establish the stoichiometric relationship between amino acid incorporation and Na ion, K ion and Cl minus fluxes. Attempts will be made to isolate and characterize one or more carriers for amino acids from these vesicle preparations. The ion fluxes will be examined using radioisotopes 22 Na ion, 42 K ion and 36 Cl minus. Uptake will be followed by trapping the vesicles on membrane filters and determining the radioactivity retained. The carrier will be enriched for on the assumption that the active molecule will specifically bind the amino acid or ion in question and thus remain attached to an affinity column. The usual techniques of protein purification will be used e.g., chromatography, electrphoresis and ultracentrifugation.